The present invention relates generally to a remover, and more particularly to a particle remover that removes particles adhered to a reticle for an exposure apparatus that manufactures such devices as a single crystal substrate for a wafer, and a glass plate for a liquid crystal display (“LCD”). An application of the inventive particle remover is not limited to an exposure apparatus. Rather, the particle remover can be broadly applied to such optical apparatuses, as photoengraving, measuring projectors, motion picture projectors, and other projectors.
In manufacturing fine semiconductor devices, such as a semiconductor memory and a logic circuit, using the photolithography technology, a reduction projection exposure apparatus has conventionally been employed which uses a projection optical system to project a circuit pattern of a mask or a reticle onto a wafer, etc. to transfer the circuit pattern.
The minimum critical dimension (“CD”) to be transferred by the projection exposure apparatus or resolution is proportionate to a wavelength of light used for exposure, and inversely proportionate to the numerical aperture (“NA”) of the projection optical system. The shorter the wavelength is, the better the resolution is. In order to meet the recent demand for finer processing to semiconductor devices, use of exposure light that has a smaller wavelength have been promoted from an ultra-high pressure mercury lamp (such as the i-line with a wavelength of approximately 365 nm) to the KrF excimer laser (with a wavelength of approximately 248 nm) and the ArF excimer laser (with a wavelength of approximately 193 nm).
However, the lithography using the UV light has the limit to satisfy the rapidly promoting fine processing of a semiconductor device, and a reduction projection optical system using extreme ultraviolet (“EUV”) light with a wavelength of 10 to 15 nm smaller than that of the UV light has been developed for efficient transfers of a very fine circuit pattern of 0.1 μm or less.
The exposure apparatus is required to accurately transfer the reticle pattern onto the substrate, and the conventional reticle has a pellicle so as to prevent particles that deteriorate the pattern transfer from adhering to the reticle. The pellicle is a thin film having high transmittance to the exposure light, a predetermined distance apart from the reticle. FIG. 13 is a schematic sectional view of the conventional reticle 1000 having a pellicle 1300. The reticle 1000 includes, as shown in FIG. 13, a substrate 1100, an absorber 1200, and the pellicle 1300. Exposure light EL is irradiated onto the reticle 1000, diffracted by the absorber 1200, generates diffracted light DL, and enters a projection optical system. Particles MP adhered to the pellicle 1300 are a predetermined distance apart from the reticle pattern or the absorber 1200, and are not imaged on a wafer due to defocus.
However, all the materials have high absorptance to the EUV light in the EUV exposure apparatus, and there are practically no materials usable for the pellicle. Accordingly, a configuration that removes a pellicle from a reticle is considered for the EUV exposure apparatus.
FIG. 14 is a schematic sectional view showing a reticle 2000 applicable to the EUV exposure apparatus. The reticle 2000 includes a substrate 2100 having a reflective multilayer film or coating, and an absorber 2200. The exposure light EL is irradiated into the reticle 2000, and generates the diffracted light DL via the reticle pattern or the absorber 2200. The particles MP that adhere to the reticle 2000 cause patterning defects that remarkably lower the yield of the manufactured semiconductor device. One proposal to reduce particle adhesions to the reticle uses a photoelectron method using the thermophoretic and/or electrostatic force. See, for example, D. J. Rader, D. E. Dedrick, E. W. Beyer, A. H. Leung and L. E. Klebanoff, “Verification studies of thermophoretic protection of EUV masks,” Emerging Lithographic Technologies VI, SPIE Proceedings Vol. 4688 (2002), and R. Moors, G.-J. Heerens, “Electorostatic mask protection for extreme ultraviolet lithography”, Journal of Vacuum Science & Technology B, Vol. 20, No. 1, pp. 316-320 (2002).
Another proposed particle removing technology is removing particles inside the exposure apparatus. For example, Japanese Patent Application, Publication No. 5-100182 proposes the removing technology of the particles or absorptive materials by using the light and by activating a collector having a transparent characteristic. The optical trap technology that condenses a laser beam and removes the particles utilizing the light intensity gradient near the condensing point is disclosed, for example, by Karel Svoboda and Steven M. Block, “Optical trapping of metallic Rayleigh particles,” Optics Letters, vol. 19, No. 13, 1 Jul. 1994, and Arthur Ashkin, “Optical trapping and manipulation of neutral particles using lasers,” Proc. Natl. Acad. Sci. U.S.A. Vol. 94 pp. 4853-4860 (1997). The particle removing technology through the laser shock wave is disclosed, for example, in Andrew C. Tam, Wing P. Leung, Werner Zapka and Winfrid Ziemlich, “Laser-cleaning techniques for removal of surface particulates,” J. Appl. Phys. 71(7), 1 Apr. 1992, although the technology is not for the reticle used for the EUV exposure apparatus. However, the prior art cannot satisfactorily remove the particles from the reticle, resulting in defects in the transferred pattern and lowered throughput due to a long time to remove the particles.
For example, Japanese Patent Application, Publication No. 5-100182 requires one collector for each absorptive material and is limited by the size of the collectable particle. In addition, when a particle is located, for example, between two adjacent convexes, in a solid structure (solid protruding artifact) that has a non-flat or undulating surface, the solid structure may obstruct the collection. Moreover, a method of removing a particle by irradiating the light onto it in one direction does not work if a structure blocks the light before the particle and cannot remove the particle.
Furthermore, the prior art reference entitled “Laser-cleaning techniques for removal of surface particulates” problematically causes damages of the reticle in removing the particles from it.